Eddy current separators have previously been known for separating non-ferromagnetic particles such as disclosed by U.S. Pat. Nos. 4,834,870 Osterberg et al. and 4,869,811 Wolanski et al. Such separators generate a rapidly changing high flux density primary magnetic field through which the non-ferromagnetic particles are conveyed. This changing magnetic flux induces eddy current flow in electrically conductive particles and thereby generates particle magnetic fields repelled by the primary magnetic field. For ferromagnetic particles, the ferromagnetic attraction is stronger than the eddy current repulsion and such particles are thus attracted to the separator. However, non-ferromagnetic particles, after passing through the primary magnetic field, are propelled varying distance depending upon the electrical resistance thereof and consequent electrical flow that divides different levels of particle magnetic fields for the different materials.
Other separators for separating non-ferromagnetic particles are disclosed by German Offenlegungsschrift DE 3416504 Wagner and European patent publication 83445 Steinert Electromagnetbau GmbH. These additional disclosures disclose such separation with falling particles.
Many conventional eddy current separators utilize a rotor having permanent magnets that generate the rapidly changing high flux density primary magnetic field. While new rare earth magnetic materials such as Neodymium-Iron-Boron and new rotor designs permit achievement of higher magnetic fields and higher rates of change of the flux than is possible with prior designs, only a small fraction of the primary magnetic field potential is actually utilized to propel the metallic particles. This is because as the particles enter the primary magnetic field, the repulsive eddy current force lifts the particles and prevents them from entering the stronger portions of the magnetic field. More specifically, conventional eddy current separators have the particles approaching the primary magnetic field generator angularly on the surface of a conveyor belt. The particles are thus conveyed into the primary magnetic field by their momentum and are held down by the force of gravity. Due to the laws of physics, the maximum force that the primary magnetic field can exert on the metallic particles is limited to that required to overcome gravity and change the particle momentum. The net result is that the particles lift off the conveyor belt before reaching the strongest location of the primary magnetic field and hence do not experience the full potential of the primary magnetic force that could be applied to them.